Nanostructured Composites Based on Graphene and Cobalt Nanoparticles in Monoamine Oxidase Biosensors for Determining Antidepressants

Amperometric monoamine oxidase biosensors based on screen-printed graphite electrodes modified with nanostructured reduced graphene oxide (RGO) composites and cobalt nanoparticles (CoNPs) were developed to determine antidepressant drug substances (tianeptine, thioridazine, and fluoxetine). Carbon nanomaterials with metal nanoparticles (nanocomposites) allow individual components to retain their properties but also ensure better quality of devices owing to joint contribution of constituents. The nanomodifier was applied to the surface of screen-printed graphite electrodes via dropwise evaporation. The RGO fastening on the surface is due to electrostatic interaction between RGO carboxyl groups and amine groups of the amine derivative on the platform of polyester polyol (H20–NH₂). Cobalt nanoparticles were obtained using the electrochemical chronoamperometry method at a potential E = –1.0 V and different times of their accumulation (50 and 60 s) on the electrode surface. According to atomic force microscopy data, the CoNP size varies with the time of electrochemical deposition of NPs, achieving predominately (40 ± 2) and (78 ± 8) nm. The electrochemical impedance spectroscopy reveals the lowest values of the charge transfer resistance for RGO-chitosan/CoNP nanocomposites and RGO-amine derivative on the polyester polyol (H20–NH₂)/CoNPs platform. The use of these nanocomposites in the electrode surface modification was found to significantly improve the analytical characteristics of biosensors, extending the operating concentration range from 1 × 10^–4 to 5 × 10^–9 mol/L, increasing the sensitivity and correlation coefficients, and decreasing the detectable concentration limit. Biosensors were shown to be promising in the quality control of antidepressants upon the determination of the main active substance in medicinal drugs and biological fluids. The lower limit of detectable concentrations of (7–9) × 10^–10 mol/L is attained by using tyramine as a substrate for the determination of fluoxetine, thioridazine, and tianeptine.